Sporadic transmission of highly pathogenic avian influenza (HPAI) H5N1 viruses from birds to humans has resulted in many deaths. Person to person transmission of the H5N1 virus has been inefficient so far, but a possible mechanism for the virus to acquire efficient person to person transmission capacity would be its adaptation to horizontal transmission in pigs. Little is known about the permissiveness of swine to infection with HPAI H5N1 viruses. Previous studies have shown that interspecies transmission of viruses can result in the rapid selection of virus variants. Our long-term goal is to study the molecular bases of a virus's ability to spread among a range of hosts and of the pathogenicity of influenza viruses. The main goal of this study is to establish the degree of permissiveness of swine to infection with Asian strains of HPAI H5N1 and their potential role in the emergence of pandemic strains. This proposal addresses the following objectives: 1) Define clinical, pathologic, immunologic responses of the host to H5N1 infection: virus ability to replicate and cause disease in pigs will be evaluated by monitoring clinical signs, measuring antibody response using hemagglutination inhibition and virus neutralization assays, and histopathology by immunohistochemistry (IHC). 2) Define a time course of 3 HPAI H5N1 virus replication and concentration of infectious virus in the major organ systems of swine: virus ability to disseminate in major organs will be evaluated by detecting antigen using IHC and the concentration of the virus by 50% egg infectious dose using standard procedures. 3) Determine sites of mucosal virus replication and shedding: virus ability to replicate in major organs is determined by detecting cellular distribution of antigen by IHC and viral RNA by in situ hybridization. 4) Determine the minimal infectious dose for 3 HPAI H5N1 strains via oral and pharyngeal exposure: This is performed by infecting pigs with doses from 1 to 4 log10 EID and determining the 50% pig infectious dose. 5) Generate starting materials to define molecular events and genetic and antigenic analyses associated with replication in swine: virus stocks & various tissue samples will be generated for further molecular analyses. Our efforts will have a major impact on the prevention and control of global outbreaks of avian influenza in animals and humans. The new knowledge gained from this study may lead to the development of novel antiviral therapies that would potentially improve human health in individuals affected by influenza. [unreadable] [unreadable] [unreadable] [unreadable]